Since there seems to be a serious ongoing dialogue here regarding the advantages or otherwise of various frac treatments I thought I'd weigh in with a few observations. Not directed at anyone in particular and mostly in a non-partisan spirit.
First let me state that there are many formations that are sensitive to "water" to a greater or lesser degree but only very few that are fatally so. There is a class of underpressured and dessicated reservoirs where the permeability is developed in micro-porosity whereby the introduction of water (in any form) is severely damaging to almost irredeemably so. (Except if you patiently wait for two or three years for the water to dry out in the reservoir by getting wicked away deep into the formation away from the well bore).
So while in strictly academic circles there has been much talk of water based formation damage - the great success of companies like Peyto and many others is that they ignored all the worry and academic problems - went ahead with massive water based fracs in sensitive formations - and the rest as they say is history.
For those very few difficult and problematic truly dessicated microporosity reservoirs - the use of distillates or propane may truly be a huge advance and make the difference between success and failure. For many others however the use of such fluids is (so far completely) unnecessary. (Even CO2 fracs are possible for genuinely difficult reservoirs without the flammability or explosion risks).
The comments about various oil companies (or drilling personnel) in downtown Calgary saying they will not go anywhere near using propane as a frac fluid - that is probably quite a realistic assessment of the zeitgeist - although there are always those looking for a new way to improve margins in any way possible. So here the point about problems with the availability of a cheap assured and non competitive water supply in certain geographical regions is a valid one. If there become places where the cost of using an effective propane frac are greatly less than the cost of using water (for whatever reasons) and the percieved risks of using that propane do not tip the balance in favour of the more costly alternative (water) then better believe it - any first movers in the propane fraccing business will flourish. (But so far - water has been much cheaper).
With regard to exactly what and how the various incidents involved in the negative publicity owe their origin to in situ hydrocarbons or introduced ones - the point is perhaps rather moot. The whole business of fracing and dealing with fluids pumped under high pressure and in high volumes is hazardous enough - especially when it is seemingly done often enough that complacency is allowed to creep in. The introduction of an extra hazard does not make the whole process any less hazardous - it always makes it much more so. Of course the protocols can and generally have been put in place to handle all these things with a high degree of safety and reliability. But there is no doubt about it - using something like propane (or distillates) for the carrying fluid medium while fracing - especially for these huge MSF frac jobs being done today - does cause a lot of people a lot of concerns about potential risks and more important the costs of liabilities and the damage to public perceptions that may ensue.
Gas fraccing technology is just another tool in the well servicing tool kit - it will have its applications and adherents. Given the right conditions and competitive price advantages its use might allow the companies specialising in its deployment to become more than small niche players.
Just my thoughts - for what they might be worth. As for explosions - that takes the presence of oxygen mixed in with the light hydrocarbons (either natural or introduced) and pressure transients. (Think diesel engine here). If there is no oxygen - there is no danger! It is that simple. The argument about whether it was well bore gases or the introduced propane is a complete red herring. (Unless you are trying to use deliberate mis-direction?)